<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
</head>
<body>


<script>
    var age =20;
    function getAge()
    {
        age = 30;
        alert(this.age);
    }
    delete window.age;
    alert(window.age);
    getAge();
    window.getAge();
</script>

</body>
</html>